The proportion of waste paper or the like included in municipal waste is tending to become higher these days. Heretofore, the recovery of such waste paper as crude pulp stock has been effected by utilization of a hydrapulper such as, for example, shown in U.S. Pat. No. 3,549,092, in the name of Joseph Baxter, Jr., issued on Dec. 22, 1970, wherein all the municipal waste is agitated in an aqueous medium or water so as to make a slurry.
However, if such a system is employed where waste includes a relatively high percentage of garbage, the discharge will create a problem, since the BOD (Biochemical Oxygen Demand) value of an aqueous medium or water used as a medium for separating crude pulp stock becomes high and, therefore, post-treatment of the used water is necessary to avoid pollution or nuisance. Further, in the case the ratio of garbage to paper or the like in municipal waste is relatively high, the recovery rate of crude pulp stock from the waste by the conventional process referred to above is expected to become lower, since the amount of crude pulp stock adhering to materials to be separated from pulp stock will increase in proportion to the increase of the ratio of garbage to paper or the like in the waste. In addition to the above drawbacks, a complicated dewatering apparatus is required in order to directly incinerate or heat-decompose the separately removed materials as they are extracted from the slurry because the removed materials contain a large quantity of water and, thus, cause great heat-loss in the process of incineration or heat-decomposition. Also, such a dewatering apparatus as above or other devices will become necessary when the recovered crude pulp stock is transported to a paper mill company.